Practical: Investigating Respiration (Edexcel IGCSE Biology: Double Science)

• We can investigate the production of carbon dioxide and heat from respiration through experiments using germinating seeds or other living organisms such as woodlice

Practical investigation: demonstrating the production of carbon dioxide

Apparatus

• Boiling tubes
• Rubber bungs
• Hydrogen carbonate indicator solution
• Cotton wool
• Glass beads
• Germinating seeds
• Boiled/dead seeds

Method

• Measure out 10 cm³ of hydrogencarbonate indicator into 3 boiling tubes
• Put in a layer of cotton wool
• Place 10 germinating seeds in tube A
• Place 10 boiled/dead seeds in tube B
• Place 10 glass beads in tube C
• Seal each tube with a rubber bung
• After 3 hours, observe the colour of the indicator

Hydrogencarbonate indicator

• Hydrogencarbonate indicator is red in atmospheric CO₂ levels
  • In high CO₂ levels the indicator reacts to CO₂ dissolving in water, which forms carbonic acid and changes the pH, causing it to become yellow
  • In low CO₂ levels the lack of CO₂ makes the solution more alkaline, causing the colour to shift to purple

Colour results for hydrogen carbonate indicator

Results

• In this investigation, we would expect to note the following
  • Tube A should turn yellow as the seeds are respiring and producing carbon dioxide
  • Tube B should remain red as the dead seeds produce no carbon dioxide
  • Tube C should remain red as there is no living material in there

Experiment to demonstrate the production of carbon dioxide by living material during respiration

Practical investigation: demonstrating the production of heat

Apparatus

• Vacuum Flasks
• Thermometer
• Cotton wool
• Germinating seeds
• Dead/boiled seeds

Method

• Set up the flasks as shown in the diagram
  • Flask A with the dead seeds
  • Flask B with the germinating seeds
• Make sure the cotton wool is plugging the top of each flask
• Hold the thermometer in place with the cotton wool
• Invert the flask
• Record the initial temperature
• After 4 days, record the final temperature

Experiment to demonstrate the production of heat by living material during respiration

Results

• The thermometer in the flask with the germinating seeds (Flask B) should show an increase in temperature
• Flask A should remain at room temperature
• This is because the seeds in flask B are respiring and producing heat energy in the process
• This shows that respiration is an exothermic reaction
• The seeds in flask A are not respiring because they are dead, so the temperature remains the same

Applying CORMS evaluation to practical work

• When working with practical investigations, remember to consider your CORMS evaluation

CORMS evaluation

• In the first investigation, your evaluation should look something like this:
  • Change - We will change the content of the boiling tube (germinating seeds, dead seeds or glass beads)
  • Organisms - The seeds used should all be of the same age, size and species
  • Repeat - We will repeat the investigation several times to ensure our results are reliable
  • Measurement 1 - We will observe the change in the hydrogen carbonate indicator
  • Measurement 2 - ...after 3 hours
  • Same - We will control the volume of hydrogen carbonate indicator, the number of seeds/beads, the temperature of the environment
• For the second investigation, your evaluation should look something like this:
  • Change - We will change the content of the flasks (germinating seeds or dead seeds)
  • Organisms - The seeds used should all be of the same age, size and species
  • Repeat - We will repeat the investigation several times to ensure our results are reliable
  • Measurement 1 - We will observe the change in the temperature on the thermometer
  • Measurement 2 - ...after 4 days
  • Same - We will control the number of seeds, the starting temperature of the flasks, the material and size of the flasks